1. Technical Field
The present invention relates to a method for removing a formation of an oxide of titanium that is generated as a byproduct of a process that forms cobalt disilicide within an insulated-gate field effect transistor.
2. Related Art
Integrated circuits constructed on silicon substrates are limited in performance by the resistance of the source, drain, and gate of a field effect transistor (FET). This difficulty may be addressed by forming cobalt disilicide areas within FETs, since the cobalt disilicide areas have low electrical resistance. For example, cobalt disilicide within the source and drain of an FET lowers the total resistance for current flow from a contact, through the FET source, into the FET channel, and out of the FET drain.
In the formation of cobalt disilicide, it is well known to utilize a layer of cobalt as a source for the cobalt disilicide and to use a titanium nitride (TiN) capping layer to protect the cobalt from oxidizing during a subsequent annealing step. After a first annealing step, this sacrificial TiN capping layer is chemically removed by a selective etch with a solution such as one comprising hydrogen peroxide. Discrete portions of the TiN cap are not always removed by this process, however, and a residual configuration, or “stringer,” of one or more oxides of titanium, such as titanium dioxide, may remain after the cobalt disilicide is formed in a second annealing step. Unfortunately, the stringer of a titanium oxide is electrically conductive and may cause electrical shorting of adjacent structures. For example, the stringer may cause a short between the gate and the drain of an FET, between the source of a first FET and the drain of a second FET, or between the drain of an FET and external circuitry. The prior art does not disclose a method of removing a stringer of an oxide of titanium that is generated as described above.